1. Field of Invention
This apparatus allows limits to be set for the adjustment range of a flow rate control knob on a welding shielding gas control device to reduce gas waste and prevent entrained air in the shielding gas stream caused by excessive flow rates.
2. Background
Gas metal arc welding (GMAW) is the official American Welding Society designation for one of the most common welding processes. It is often called MIG welding or wire welding. GMAW will be used in this text. Gas tungsten arc welding (GTAW) is the official American Welding Society designation for a commonly used welding process. It is often called TIG welding. GTAW will be used in this text. In the GMAW process, molten metal is produced by an electric arc. A welding wire is fed into the arc zone by a feeding mechanism, through what is referred to as a welding torch. A suitable power source is connected between the workpiece to be welded and the welding wire passing through the welding torch producing the arc. Molten metal comprising the weld is derived from the materials to be welded and the welding wire being fed though the welding torch. In the GTAW process, molten metal is also produced by an electric arc. An essentially non-consumable tungsten electrode is located in what is referred to as a welding torch that is held in close proximity to the workpiece to be welded. A suitable power source is connected between the workpiece and the tungsten electrode in the welding torch producing the arc. In GTAW molten metal comprising the weld is derived from the materials to be welded and additionally in some applications from a welding rod feed into the molten weld puddle.
Both GMAW and GTAW processes utilize a shielding gas to protect the molten weld metal from the surrounding air. Oxygen, nitrogen as well as hydrogen from the moisture in the air cause significant problems in weld metal. This shielding gas may be argon, carbon dioxide, helium or mixtures of these and small amounts of other gases. This shielding gas is usually transported in a flexible hose to and through the welding torch. It exits the welding torch in a tubular device surrounding the wire or tungsten electrode. In GMAW this device is often made of a copper alloy and is called a nozzle. In the GTAW process the shielding gas exits most often through a ceramic cylindrical device referred to as a gas cup. The shielding gas is usually supplied from a high-pressure gas cylinder or a pipeline. The welding operator is often required to set the shielding gas flow rate utilizing a shielding gas flow control mechanism. One type of such mechanism employs a needle valve for gas flow adjustment. The flow rate required is dependent on a number of variables including the specific gas mixture but generally ranges from a low of approximately 5 liters per minute (10.6 cubic feet per hour) for GTAW to a high of about 24 liters per minute (51 cubic feet per hour) for GMAW. When helium gas mixtures are used the flow rates may be considerably higher than those mentioned. Because of the significantly different flows required, needle valve controls must have a wide range of operation. These needle valve devices are often designed to handle a variety of gases and if on a pipeline gas supply the various pipeline pressures that might be encountered. Therefore particularly with gases of higher density, such as argon or argon rich mixtures, they often allow much higher flow rates than are desirable. This enables the welding operator to set flow rates much higher than needed.
If the flow rates are set at too low a level there will be insufficient gas available to adequately shield the molten weld puddle. Certain welding joint designs such as when joining two perpendicular plates (referred to as a fillet weld) allow the use of lower gas flow rates since the members being welded help contain the shielding gas. Therefore it is desirable to allow the welding operator the ability to have some control of the shielding gas flow so they can adjust flow levels to fit the particular welding applications.
The maximum desirable gas flow rate is dependent on a number of variables including the diameter of the shielding nozzle or cup and the specific torch design. For example, if the flow rate in a GMAW torch utilizing argon, carbon dioxide or mixtures of these gases exceeds about 28 liters per minute (60 cubic feet per hour) the exiting, gas flow will be turbulent versus the desired laminar flow. Turbulent flow causes air to be entrained into the shielding gas stream. The weld quality will be degraded due to the molten weld metal absorbing oxygen or nitrogen from the air. When welding steel, moisture from the air will break down into hydrogen that is readily absorbed in molten steel. As the weld puddle cools the presence of hydrogen may cause small holes referred to as porosity or cracks. Nitrogen may also cause porosity and when welding steel it forms very hard metallurgical constituents making the steel brittle. Excess oxygen can cause a number of problems with a common one being porosity when it combines with the carbon in the steel forming carbon monoxide gas holes.
The use of excessive flow rates wastes significant shielding gas. Unfortunately welding operators often follow the adage that “if some shielding gas is good more must be better.” It has been observed that many welders are utilizing twice the amount of shielding gas flow they should. An article in the June, 2000 Fabricator Magazine entitled “Shielding Gas Consumption Efficiency,” page 27, col. 2 & 3 sites the fact that most shops are using from about two to over ten times more gas than is possible. In the same article page 28, col. 3, third paragraph states; “some welders think that if a little bit is good, then a lot is even better.” This reinforces the lack of understanding of the quality problems associated with high gas flow in addition to indifference about using excess shielding gas. An article was published in the January, 2003 issue of Trailer Body Builders Magazine entitled “How to Save 20% on Welding Costs.” On page 46, col. 3 of this article a representative from a leading manufacturer of shielding gases is quoted as saying, “A minimum of 142 liters (5 cubic feet) of gas is required to weld 0.45 kilograms (one pound) of wire, but the industry average usage is 850 liters (30 cubic feet).” Since it is very unusual to need more than about 225 to 280 liter (8 to 10 cubic feet) of shielding gas per 0.45 kilograms (one pound) of wire this statement means the average user consumes from three to six times the amount of shielding gas theoretically needed. In the article the representative from the manufacturer of welding gases on page 46, col. 3 states from his observation “welders typically use an excessive amount of shielding gas, thinking “if a little is good more must be better.”” This reinforces that welders setting excessively high shielding gas flow rates is a significant cause of gas waste. Using the lower mentioned value of 3 times theoretical need for the average usage and estimating the average retail price and annual volume;
American consumers are wasting over 750 million to one billion dollars annually in shielding gas employed for GMAW and GTAW.
3. Description of Prior Art
There are several devices employed which limit the flow of shielding gas flow when using a needle valve type flow control mechanism:    (a) One method occasionally used to limit the maximum shielding gas flow rate is to incorporate a flow-control orifice at the output port of a flow control mechanism or close to the solenoid used to turn the gas flow off and on. Hanby in U.S. Pat. No. 6,390,134, issued on May 21, 2002, defines the use of restrictors to control shielding gas flow. Hanby states in col. 2, 7 to col. 2, 9, “Gas-flow may be set to any level below the maximum threshold by adjusting the flowmeter, just as in normal welding operation.” Instructions for the use of a product listed as produced utilizing this patent were presented on Internet web site http://www.surgeandsave.com on Jan. 6, 2006. These instructions describe a complicated procedure for selecting the proper orifice size. It is not clear if the orifice is being sized to control the steady state flow or if only the surge flow due to pressure build-up in the gas delivery hose is being addressed with this device. The method of controlling the maximum flow in either situation requires trial and error and is not readily usable for the average production-welding situation. Controlling flow with an orifice that is mechanically added external to the flow control or at the end of the gas delivery hose creates other problems. Orifice type devices are not practical when several types of shielding gas or gas mixtures with significantly different densities are utilized. For example, when using GTAW and welding steel, an argon shielding gas would mostly likely be employed but when welding aluminum a much less dense helium gas mixture might be used. The large differences in gas densities would require significantly different gas flow rates and therefore different orifice sizes to produce these flow rates.    (b) Another method employed by one manufacturer of needle valve shielding gas flow controls provides a locking flow control knob that replaces the knob supplied with the flowmeter/flow-control mechanism. A description of this device is referenced from material presented on the manufacturer's Internet Web site http:www.smithequipment.com/products/regul/flowmeters.htm on Jan. 6, 2006. The device simply locks the knob from turning. This requires mechanically disassembling the flow control mechanism, which some users are reluctant to perform. In addition, fully locking the flow setting may not be desirable. This does not allow adjustment by the welding operator to increase flow when necessary such as when drafts are present. Also this device is only applicable to this manufacturer's products and can not be used on the majority of flow control devices that exist and are not of this specific design. The vast majority of needle valve type flow control mechanisms that are in use in the welding industry do not have a means of controlling flow limits.